1. Field of the Invention
The present invention relates to novel methods for producing an enhanced immune response to persistent infections by the human papillomavirus.
2. Description of the Related Art
Human papillomavirus (HPV) infections are associated with a spectrum of epithelial diseases from benign warts to cervical intraepithelial neoplasia (CIN) to invasive carcinoma. Additionally, HPV infection is found in more than half of the patients with colorectal cancer (Bodaghi et al. 2005 Clin. Cancer Res. 11:2862-2867). Almost all cervical cancer is caused by HPV infection, most often HPV16 (Frazer, 2004 Nat. Rev. Immunol. 4:46-54). In developing countries, cervical cancer is often the most frequent female malignancy and constitutes up to a quarter of all female cancers (Pisani et al. 1999 Int. J. Cancer 83:18-29; Parkin 1999 CA Cancer J. Clin. 49:33-64). In light of these facts, the development of effective HPV vaccines could contribute greatly to the prevention and treatment of cervical cancer. Substantial advances have been made in developing HPV prophylactic vaccines based on L1 virus-like particles (VLPs) that induce neutralization antibody to L1 (Villa, L. L. et al. 2005 Lancet Oncol. 6:271-278; Schiller, J. T. et al. 2001 Expert Opin. Biol. Ther. 1:571-581; Lowy, D. R. et al. 2003 J. Natl. Cancer Inst. Monogr. 111-116; Koutsky, L. A. et al. 2002 N. Engl. J. Med. 347:1645-1651). It has been shown that HPV 16 VLPs can generate high titers of virus-neutralizing antibodies, and they have been 100% effective at preventing persistent HPV 16 infection in clinical trials (Frazer 2004 Nat. Rev. Immunol. 4:46-54). By contrast, therapeutic HPV vaccines have not yet demonstrated high efficacy against cervical cancer or premalignant HPV-induced neoplasia in clinical trials (Stanley 2003 Expert Rev. Vaccines 2:381-389). An effective combined prophylactic/therapeutic vaccine would be especially attractive for cervical cancer prevention. It could promote mass immunization programs of both preadolescent and older women, many of whom have already been exposed to genital tract HPV infection, and thereby promote more rapid development of effective immunity. A combined vaccine could offer the best combination of immediate impact and long term effectiveness. It will be particularly useful in developing countries, where most women with prevalent infection do not have access to quality Pap screen programs to reduce their risk of cervical cancer (Schiller, J. T. et al. 2004 Nat. Rev. Microbiol. 2:343-347).
HPV E6 and E7 are constitutively expressed in cervical cancer cells, and therefore provide attractive targets for a therapeutic vaccine. Therapeutic vaccine strategies targeting E6 and E7 have included peptides (Ressing et al. 1995 J. Immunol. 154:5934-5943), recombinant E6 and E7 proteins (Fernando et al. 1999 Clin. Exp. Immunol. 115:397-403), viral vectors (Velders et al. 2001 Cancer Res. 61:7861-7867), and plasmid DNA (Eiben et al. 2002 Cancer Res. 62:5792-5799; Shi et al. 1999 J. Virol. 73:7877-7881).
During the HPV infection, the HPV16 E2 gene is likely uniformly expressed during the productive viral infection in CIN1 and CIN2 (Hegde, R. S. 2002 Annu. Rev. Biophys. Biomol. Struct. 31:343-360). HPV 16 E6 and E7 genes are expressed in CIN2, CIN3 and cervical cancer cells, and have been the main focus of HPV therapeutic vaccines.
The E2 gene is highly expressed in low grade CIN, and lost when the lesion progresses to invasive carcinoma (Stevenson, M. et al. 2000 J. Gen. Virol. 81:1825-1832). In a cottontail rabbit papillomavirus (CRPV) model, immune response against E2 is associated with spontaneous regression of papillomas (Selvakumar, R. et al. 1995 Virology 208:298-302). Therefore, E2 and E7 provide attractive targets for a therapeutic vaccine with treatment ranging from low-grade diseases, such as CIN, VIN, and AIN, to malignant carcinoma (Rosales, C. et al. 2000 Cancer Immunol Immunother. 49:347-360; Eiben, G. L. et al. 2003 Viral Immunol. 16:111-121). Vaccine strategies targeting E6 and E7, using peptides (Ressing, M. E. et al. 1995 J. Immunol. 154:5934-5943), proteins (Fernando, G. J. et al. 1999 Clin. Exp. Immunol. 115:397-403), viral vectors (Velders, M. P. et al. 2001 Cancer Res. 61:7861-7867) and plasmid DNA (Shi, W. et al. 1999 J. Virol. 73:7877-7881; Moniz, M. et al. 2003 Front. Biosci. 8:d55-68), have been reported. However, there is only limited information on the CD8+ T cell response to E2 (Rosales, C. et al. 2000 Cancer Immunol. Immunother. 49:347-360; de Jong, A. et al. 2002 Cancer Res. 62:472-479). Therefore, development of a vaccine targeting E2 would be useful in the treatment of low-grade diseases caused by HPV infection, such as CIN, VIN, and AIN, and in the prevention of the subsequent development of HPV-associated anogenital cancers.
Experimental evaluation of therapeutic HPV vaccine strategies has involved C57BL/6 mice and H-2Kb restricted T cell epitopes (Feltkamp 1993 Eur. J. Immunol. 23:2242-2249). These studies have provided limited predictive value regarding HLA-restricted responses in humans. However, HLA-A2 transgenic mice have been used to evaluate the presentation of chimeric VLP epitopes by a human MHC-1 molecule. It has been shown that CD8+ T cells from HLA-A2 mice recognize the same HLA-A2-restricted peptides as are recognized by human T cells (Ressing et al. 1995 J. Immunol. 154:5934-5943; Eiben et al. 2002 Cancer Res. 62:5792-5799). These studies indicate the efficacy of using HLA-A2 transgenic mice to evaluate the strategies for vaccine development.
In mice, chimeric VLPs have been shown to induce HPV16-neutralizing antibodies and immune responses against challenge by synergistic tumor cells expressing E7 (Frazer 2002 Virus Res. 89:271-274; Pastrana 2001 Virology 279:361-369). In addition, chimeric VLPs were able to induce T cell responses, in the absence of a conventional adjuvant, such as Incomplete Freund's Adjuvant (IFA). VLPs are bound and internalized by monocytes, macrophages and myeloid dendritic cells (DCs) in vitro (Storni et al. 2002 J. Immunol. 168:2880-2886; Da Silva 2001 Int. Immunol. 13:633-641).
Therefore, the development of optimized immunization strategies for use in combination with HPV VLP and other HPV immunogens is a critical need. The invention described herein is directed to address this and other needs.